Extension of catalyst cycle length in residuum desulfurization processes

ABSTRACT

Solvent injection in amounts no greater than 2 wt % can favorably alter the way heavy metals, such as vanadium, are normally deposited in catalyst particles. Heavy metals may be stored on the catalyst in a more compact form, saving catalyst pore volume. Consequently catalyst cycle length is improved, since capacity for deposition is increased.  
     The instant invention has also been demonstrated to control the rate of catalyst fouling by deposition of coke, or microcarbon residue (MCR). In the past, attempts to increase catalyst activity led to increased rates of catalyst fouling and shorter catalyst life. In the instant invention the rate of deposition of microcarbon residue is decreased, resulting in slower fouling of pores and increased cycle length.

[0001] This application claims priority from U.S. ProvisionalApplication Serial No. 60/230,646, filed Sep. 7, 2000.

FIELD OF INVENTION

[0002] This invention is concerned with a process for the extension ofcatalyst cycle length when employed in residuum hydrodesulfurizationprocesses.

BACKGROUND OF THE INVENTION

[0003] Catalyst poisoning has long been a problem inhydrodesulfurization of residuum and heavy oils. These feeds oftencontain organometallic compounds, such as nickel and vanadium. Thesemetallic impurities are thought to deposit on the surface and in thepores of the hydrodesulfurization catalyst. Catalyst poisoning has beenknown to decrease catalyst activity, particularly if dissolved metalssuch as nickel and vanadium are present in amounts greater than 10 to 20ppm.

[0004] U.S. Pat. No. 5,215,955 (Threlkel) attempted to solve the problemof fouling by the use of a catalyst having a minimum number ofmacropores. Less than 2% of the pore volume of the catalyst of Threlkelmay possess a diameter greater than 1000Å. This catalyst contains GroupVIB and Group VIII metals on a support comprising alumina. At least 80%of the pore volume comprises pores having a diameter between 110 and190Å. In addition to increased activity, this catalyst was known to haveincreased life and increased metals capacity. This solution did limitresiduum processing to the use of specific catalysts, however.

[0005] Other approaches have been used over the years to enhancecatalyst effectiveness in hydrodesulfurization processes, among them“solvent injection.” Though the concept of “solvent injection” intoresiduum hydroprocessing units is not new, and has actually beenpracticed commercially for many years in a number of units, its impacton catalyst performance has actually been very poorly understood. Themost common solvent has always been water. If used in large amounts,however, solvent injection could create deleterious side effects.

[0006] U.S. Pat. No. 4,013,637 (Eberly, Jr.) discloses ahydrodesulfurization process in which water is employed. Theeffectiveness of the process is improved by injecting 1-32 volumepercent in the gas phase of the reaction zone. The feed however,contains substantially no metals. The intent of the instant inventionemploys water to enhance catalyst life when feeds containing heavymetals are being desulfurized.

[0007] GB 1468160 and GB 1505886 are commonly owned and discloseprocesses for catalytic hydrodesulfurization in the presence of watervapor of oils containing vanadium and nickel, without catalystreplenishment. These inventions possess specific requirements concerningwater vapor partial pressure and the ratio between average pore diameterand average particle diameter for the catalyst or catalyst combinationemployed. Another commonly owned patent, GB 1525508, also disclosescatalytic desulfurization employing water, or another solvent, such as alower alcohol or other water precursor.

[0008] U.S. Pat. No. 4,052,295 (Pronk) discloses a process for catalytichydrodesulfurization of vanadium-containing heavy hydrocarbon oils.Heavy hydrocarbon oil containing vanadium is contacted at elevatedtemperature and pressure with hydrogen and with a catalyst. The catalystis loaded with nickel and/or cobalt and with about 2.5 to 60 parts byweight of molybdenum and or tungsten on a porous carrier such asalumina. No water vapor is added until the average vanadium content ofthe catalyst has increased during the contacting by at least 5 parts byweight per 100 parts by weight. Pronk states that the use of water vaporcan be used effectively toward the end of a desulfurization operationwhich has been operated in the absence of added water vapor when thetemperature has been raised to the maximum allowable level and operationunder normal circumstances would have to be terminated.

[0009] Pronk points out problems that arose in its invention with theuse of water vapor in hydrodesulfurization of heavy oils containingvanadium or other heavy metals. The use of water vapor, according toPronk, requires extra energy to evaporate the requisite quantity ofwater, resulting in a rise of costs associated with desulfurization.Furthermore, Pronk found, in order to ensure that the process be carriedout at a constant total pressure, the hydrogen partial pressure must bereduced if the desulfurization is carried out in the presence of watervapor. Reduction of the hydrogen partial pressure generally results inlower catalyst activity. For these reasons water was added at a certainstage in the process, but not initially. In the instant invention it ispreferable to add water early in the operational cycle in order tomaximize metals deposition. Metals are deposited constantly throughoutthe cycle if water deposition begins early.

[0010] U.S. Pat. No. 3,501,396 (Gatsis) discloses a process for thedesulfurization of petroleum crude oil, which comprises admixing thecrude oil with hydrogen and from 2 to 30 wt % water and reacting theresultant mixture in contact with a catalytic composite at desulfurizingconditions. The patent states that utilization of water in thesecomparatively excessive amounts appears to improve the hydrogendiffusion rate through the liquid phase on the catalyst, being increasedas a result of the reduced viscosity and surface tension characteristicsof the liquid phase. The difficulty of supplying hydrogen to the activesites of the catalyst is greatly reduced, and catalytic stability andincreased. There is no mention in U.S. Pat. No. 3,501,396 of extensionof catalyst life. Furthermore, the instant invention obtains itsbenefits using no more than 2 wt % water.

[0011] U.S. Pat. No. 3,753,894 (Shoemaker et al.), discloses ahydrodesulfurization process for processing a sulfur-containing residuumfeed, wherein water is injected between the several catalyst beds of amulti-bed reactor to quench the products of the reaction andsimultaneously to suppress deactivation of the catalyst, particularly asoccurs during the initial period of a production run. Water may be addedin concentrations as high as 50 wt %. As these references demonstrate,it was commonly believed that solvent injection induced slight benefitsin catalyst activity, particularly concerning sulfur or heavy metalsremoval and to a lesser degree the removal of microcarbon residue.Conditions, feeds, and catalysts useful in these inventions werespecifically limited, however. Often solvents such as water were used inlarge amounts. Finding a process in which the optimal amount of solventcould be used would reduce the need for process modifications, simplifydownstream processing, decrease operating costs, and lessen hydrogenpartial pressure penalties.

SUMMARY OF THE INVENTION

[0012] Catalyst fouling by heavy metals, such as vanadium, may beinhibited by the injection of an effective amount of solvent during theresiduum hydrodesulfurization process or just prior to it. Waterinjection aids in the control of the temperature increase requirementover time. Water injection results in a more uniform deposition ofmetals such as vanadium within the catalyst pellets, thereby delayingthe onset of pore mouth plugging.

[0013] The most preferred solvent is water. The process of the instantinvention has been found to operate effectively under a wide variety ofconditions and with a wide variety of feeds and catalysts.

[0014] In the past as the references in the Background of the Inventiondemonstrate, water in relatively large quantities was added in order toincrease catalyst activity. Recent findings have shown that the mostinteresting aspect of solvent injection in specific amounts is notactually its relatively minor impact on catalyst activity, but itssignificant impact on catalyst cycle length. Solvent injection inamounts no greater than 2 wt %, results in a controlled temperatureincrease across the reactor, and can favorably alter the way heavymetals, such as vanadium, are normally deposited in catalyst particles.Heavy metals may be stored on the catalyst in a more compact form,saving catalyst pore volume. Consequently catalyst cycle length isimproved, since capacity for deposition is increased.

BRIEF DESCRIPTION OF THE FIGURES

[0015]FIG. 1 demonstrates the effect that the introduction of 2 wt %water 200 hours into the operation cycle has on the temperature increaserequirement over time, as compared to an operation cycle with no waterinjection. The normalized temperature of about 730° F. levels out atapproximately 800 hours on stream. The normalized temperature is thetemperature that would be required to keep the sulfur concentration at0.55 wt %. Product sulfur concentration remains constant at 0.55 wt %until the end of the operation cycle without temperature increase.

[0016]FIG. 2 illustrates the same operational cycles as shown in FIG. 1.The concentration of vanadium in the product is lower at lower operatingtemperatures in the case, in which 2 wt % water was injected, while inthe cycle in which no water was added vanadium concentrations in theproduct were higher. This demonstrates that more vanadium is remainingon the catalyst at the end of the run and is better penetrating thecatalyst.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Solvent injection, as depicted in the instant invention, isuseful in most residuum hydroprocessing applications experiencingsignificant vanadium induced catalyst aging. Benefits are generally mostpronounced in applications with very high end of run vanadium loading,severe processing conditions, and those using catalysts with low surfaceto volume ratio. This would include catalysts used in onstream catalystreplacement (OCR) processes and other large extrudate catalysts.

[0018] Catalysts with low surface to volume ratio are generally moresensitive to pore mouth plugging, since access to the pellet interior (asignificant portion of the overall catalyst volume and surface area) ismore restricted. OCR applications combine utilization of large catalystpellets, severe operating conditions and high vanadium loading. Theconcept of solvent injection (the preferred solvent is water, althoughoxygen-containing compounds such as short chain alcohol, either or otherwater precursors may also be used) is particularly well suited to OCRtechnology.

[0019] The minimal amount of water (no greater that 2 wt % in theinstant invention) necessary to trigger the beneficial chemicalreactions is injected into the OCR reactor. Minimizing the injection ofexcess solvent to the OCR (or to a reactor in any hydrodesulfurizationprocess) is important to avoid significant process modifications,simplify downstream processing, decrease operating costs, lessenhydrogen partial pressure penalties and minimize gas rate to maintaingood flow conditions. The OCR process is more completely disclosed inU.S. Pat. No. 5,076,908 (Stangeland et al) which is hereby incorporatedby reference. As illustrated in the Examples below, highly effectiveresults are obtained when a solvent such as water is added early in theoperating cycle. Solvent may be added at any time during the operatingcycle but addition at the beginning of the cycle is preferable. TheExamples demonstrate addition of water in the first 200 hours of theoperational cycle.

[0020] Feeds suitable for use in the instant invention include “heavy”hydrocarbon liquid streams, and particularly crude oils, petroleumresidua, tar sand bitumen, shale oil or liquefied coal or reclaimed oil.Petroleum residua may be crude oil atmospheric distillation columnbottoms (reduced crude oil or atmospheric column residuum), or vacuumdistillation column bottoms (vacuum residua).

[0021] These feed streams generally contain product contaminants, suchas sulfur, and/or nitrogen, metals, including heavy metals such asvanadium and organo-metallic compounds possibly in porphyrin orchelate-type structures. Residua typically contain greater than 10 ppmmetals. These contaminants tend to deactivate catalyst particles duringcontact by the feed stream and hydrogen under hydroprocessingconditions. This invention is particularly effective with residuumfeeds, such as the Maya residuum employed in the Examples below.

[0022] The high reactivity of the Maya/Arabian Heavy Atmospheric Residuablend, coupled with high temperatures of operation, usually promotessignificant vanadium deposition on the outside of the catalyst pellets.Such deposition tends to block access of the crude to the interiorcatalytically active portion of the catalyst. In the instant invention,significant vanadium deposition has been found within the catalystitself. Catalyst life is extended significantly because the pores arenot blocked as quickly.

[0023] As further described in U.S. Pat. No. 5,215,955, typicaloperating conditions for hydrodesulfurization processes include areaction zone temperature of 600° F. to 900° F., a pressure of 200 to3,000 psig, and a hydrogen feed rate of 500 to 15,000 SCF per barrel ofoil feed. Generally such hydrodesulfurization is in the presence of acatalyst or combination of catalysts which contain Group VI or VIImetals such as platinum, molybdenum, tungsten, nickel, cobalt, etc.These metals may be loaded onto refractory supports such as alumina,silica, magnesia and so forth. A high surface to volume ratio ispreferable for the catalysts employed in this invention.

[0024] Alumina is the preferred catalytic support material althoughalumina may be combined with silica or magnesia. The support materialsare available from a variety of commercial sources, or they may beprepared as disclosed in Tamm '661. The preparation of catalystssuitable for use in the hydroprocessing of residuum is further disclosedin U.S. Pat. No. 5,620,592, U.S. Pat. No. 5,215,955 and U.S. Pat. No.5,177,047. It is notable that the catalysts disclosed in these patentspreferably have few macropores. The catalysts of the OCR process arehighly macroporous. The instant invention may thus be employed withcatalyst possessing wide variation in pore structure.

[0025] The hydrocarbon hydrodesulfurization catalysts of the presentinvention contain at least one hydrogenation agent, and preferablycontain a combination of two such agents. One or more catalysts may beused in any of the reaction zones. The metals and/or the compounds ofthe metals, particularly the sulfides and oxides of Group VIB(especially molybdenum and tungsten) and Group VII (especially cobaltand nickel) of the elements are in general satisfactory catalyticagents. The combinations of cobalt, nickel and molybdenum catalyticagents are preferred. Suitably, the Group VII metal is present in thecatalyst in the range of about 0.1 wt. % to about 5 wt. %, calculated asthe metal and based upon the total catalyst weight, and the Group VIBmetal is present in an amount within the range of about 4 wt. % to about20 wt. %, calculated as the metal and based upon the total catalystweight. The most preferred catalyst contains between about 2% and about4% nickel and between about 7% and about 9% molybdenum. The catalystsused in the Examples (Table 3) are typical.

[0026] The catalytic agents required for the present catalystcompositions may be incorporated into the calcined carrier by anysuitable method, particularly by impregnation procedures ordinarilyemployed in general in the catalyst preparation art. It has been foundthat an especially outstanding catalyst is made by a single stepimpregnation of the alumina using a solution of a cobalt or nickel saltand a heteropolymolybdic acid, for example, phosphomolybdic acid.

EXAMPLES Example I

[0027] A reactor system, consisting of three reactors connected inseries for downflow operation, was loaded with commercially availablecatalyst comprising Al/Mo/P/Ni (See Table 3). The reactor system was runat 57% MCR conversion based on a target material balance. A similaradiabatic temperature profile was established in each of the reactors.The temperature increase across each reactor was set to 50-55° F. withan overall maximum temperature of 780° F. The reactor system totalpressure was maintained at 2200 psig with a hydrogen partial pressure of1800 psia & a hydrogen flow rate of 5000 scf/bbl. The feed consisted ofArabian Heavy/Maya atmospheric residuum (See Table 1 for Feed 2 physicalproperties) fed at a liquid hourly space velocity (LHSV) of 0.46 hr⁻¹.

[0028] After 1,508 hrs on-stream in this accelerated aging regime, waterwas continuously injected at 3 wt % or 3.2 gms/hr into the feed for theremainder of the run ending at 2,806 hrs. The results from this runclearly show a significant improvement of catalyst cycle length andmetal loading. The cycle length increased by 27% as compared to the basecase reactor system, and the metal loading increased by 28% as comparedto the base case reactor system.

Example II

[0029] The reactor system and conditions were identical to Example Iabove except that the LHSV was 0.22 hr⁻¹, and Feed 2 was used. (SeeTable 1 for feed 1 physical properties).

[0030] In this example, water was continuously injected at 2.0 wt % or2.2 gms/hr into the feed at the start of the run and ending after 2380hrs. The cycle length improved by 31% and the metal loading increased by34% as compared against the base case reactor system.

Example III

[0031] The reactor system was a single stage reactor with the sameconditions as Example I except the feed was a different feed (See Table1 for feed 3 physical properties ) and only catalyst 2 (See Table 3) wasused for this run.

[0032] In this example, water was continuously injected at 1.5 wt % or1.7 gms/hr into the feed throughout the 750 hrs of run time. However,despite the short duration of this run and the relatively low catalystmetal loading there was a clear indication that a water-induced catalystmetal capacity and a lower catalyst aging rate was starting to developas compared to the base case reactor system.

Example IV

[0033] The reactor system was a single stage reactor with the sameconditions as Example I except the feed was a different feed (See Table1 for feed 3 physical properties) and only catalyst 2 (See Table 3) wasused for this run.

[0034] In this example, water was continuously injected at 1.0% or 1.2gms/hr into the feed throughout the 750 hrs of run time. Here again,given the short duration of this run, there was an indication that thewater injection was starting to improve the metal loading capacity & theaging rate of the catalyst. TABLE 1 Feed: Arab Heavy/Maya AtmosphericResiduum Feed 1 Feed 2 Feed 3 Sulfur, wt % 4.660 4.620 4.551 Nitrogen,ppm 4087 4024 4260 MCR, wt % 18.9 704.8 284.5 API 7.5 7.4 8.9 Iron, ppm5.6 8.2 7.3 Nickel, ppm 58.9 59.6 70.2 Vanadium, ppm 264.0 265.0 358.0IBF (° F.) 684 676 641

[0035] TABLE 2 Water % Run Length % Metal Load Injection Wt. ImprovementImprovement 0.75% 1.5% 2.0% +30.8% +34.0% 3.0% +26.6% +28.0% Estimatedvalues

[0036] TABLE 3 Composition Catalyst 1 Catalyst 2 Catalyst 3 Al₂O₃ 79%86% 80% MoO₃ 13% 9% 12% P₂O₅ 4% 2% 4% NiO 4% 3% 4%

What is claimed is:
 1. A process for the extension of catalyst cyclelength in the hydrodesulfurization of feeds containing heavy metalcontaminants, said process occurring in one or more reaction zones,where the feed is contacted with the hydrodesulfurization catalyst,whereby no more than 2 wt % of a solvent is mixed with the feed prior toits entry into the initial reaction zone or is subsequently added to theinitial reaction zone or a succeeding reaction zone.
 2. The process ofclaim 1, wherein the solvent is a compound comprising oxygen which isselected from the group consisting of water, alcohol, either and otherwater precursors.
 3. The process of claim 1, wherein a heavy metalcontaminant is nickel, vanadium, or a mixture of the two.
 4. The processof claim 1, wherein no more than 1.5 wt % of a solvent is mixed with thefeed prior to its entry into the initial reaction zone or issubsequently added to the initial reaction zone or a succeeding reactionzone.
 5. The process of claim 4, wherein no more than 0.75 wt % of asolvent is mixed with the feed prior to its entry into the initialreaction zone or is subsequently added to the initial reaction zone or asucceeding reaction zone.
 6. The process of claim 1, wherein the solventis injected during the first 200 hours of the operational cycle.
 7. Theprocess of claim 1, wherein the feed is selected from the groupconsisting of crude oils, petroleum residua, tar sand bitumen, shaleoil, or liquefied coal or reclaimed oil.
 8. The process of claim 7,whereby petroleum, residua is selected from the group consisting ofcrude oil atmospheric distillation column bottoms or vacuum distillationcolumn bottoms.
 9. The process of claim 8, crude oil atmosphericdistillation column bottoms. is selected from the group consisting ofreduced crude oil or atmospheric column residuum.
 10. The process ofclaim 1, whereby at least one reaction zone is designed for onstreamcatalyst regeneration.
 11. The process of claim 1, whereby the operatingconditions for hydrodesulfurization processes include a reaction zonetemperature in the range from 600° F. to 900° F., a pressure in therange of from 200 to 3000 psig, and a hydrogen feed rate of 500 to 15000SCF per barrel of oil feed.
 12. The process of claim 10, in which atleast one catalyst in one or more of the reaction zones is a macroporouscatalyst suitable for onstream catalyst regeneration.